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type=\u0022text\/css\u0022 rel=\u0022stylesheet\u0022 href=\u0022https:\/\/bmjopen.bmj.com\/sites\/default\/files\/advagg_css\/css__ZqR9oFtEjI7t5h7UPJpE0tHpaVSMTAbm0a23YsPXKOs__z0ziYHnUeoonPnsQckGJK26VB3Dp5GbBJ1xzkT0Vnb0__nl6RvPcIOPTwXmwV5KiKvhH9DVPUzvybkbbpUVu1TfM.css\u0022 media=\u0022all\u0022 \/\u003E\n\u003Clink rel=\u0027stylesheet\u0027 type=\u0027text\/css\u0027 href=\u0027\/sites\/all\/modules\/contrib\/panels\/plugins\/layouts\/onecol\/onecol.css\u0027 \/\u003E\u003C\/head\u003E\u003Cbody\u003E\u003Cdiv class=\u0022panels-ajax-tab-panel panels-ajax-tab-panel-jnl-template-bmjj-tab-art\u0022\u003E\u003Cdiv class=\u0022panel-display panel-1col clearfix\u0022 \u003E\n \u003Cdiv class=\u0022panel-panel panel-col\u0022\u003E\n \u003Cdiv\u003E\u003Cdiv class=\u0022panel-pane pane-highwire-markup author-affiliates col-narrow-12 author-affiliates-corresp article\u0022 \u003E\n \n \n \n \u003Cdiv class=\u0022pane-content\u0022\u003E\n \u003Cdiv class=\u0022highwire-markup\u0022\u003E\u003Cdiv xmlns=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022 id=\u0022content-block-markup\u0022 xmlns:xhtml=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022\u003E\u003Cdiv xmlns:xhtml=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022 class=\u0022contributors\u0022\u003E\u003Col class=\u0022contributor-list\u0022 id=\u0022contrib-group-1\u0022\u003E\u003Cli class=\u0022contributor\u0022 id=\u0022contrib-1\u0022\u003E\u003Cspan class=\u0022name\u0022\u003EA Rosemary Tate\u003C\/span\u003E\u003Ca id=\u0022xref-aff-1-1\u0022 class=\u0022xref-aff\u0022 href=\u0022#aff-1\u0022\u003E1\u003C\/a\u003E, \u003C\/li\u003E\u003Cli class=\u0022contributor\u0022 id=\u0022contrib-2\u0022\u003E\u003Cspan class=\u0022name\u0022\u003EAlexander G R Martin\u003C\/span\u003E\u003Ca id=\u0022xref-aff-2-1\u0022 class=\u0022xref-aff\u0022 href=\u0022#aff-2\u0022\u003E2\u003C\/a\u003E, \u003C\/li\u003E\u003Cli class=\u0022contributor\u0022 id=\u0022contrib-3\u0022\u003E\u003Cspan class=\u0022name\u0022\u003EAishath Ali\u003C\/span\u003E\u003Ca id=\u0022xref-aff-1-2\u0022 class=\u0022xref-aff\u0022 href=\u0022#aff-1\u0022\u003E1\u003C\/a\u003E, \u003C\/li\u003E\u003Cli class=\u0022last\u0022 id=\u0022contrib-4\u0022\u003E\u003Cspan class=\u0022name\u0022\u003EJackie A Cassell\u003C\/span\u003E\u003Ca id=\u0022xref-aff-1-3\u0022 class=\u0022xref-aff\u0022 href=\u0022#aff-1\u0022\u003E1\u003C\/a\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Col class=\u0022affiliation-list\u0022\u003E\u003Cli class=\u0022aff\u0022\u003E\u003Ca id=\u0022aff-1\u0022 name=\u0022aff-1\u0022\u003E\u003C\/a\u003E\u003Caddress\u003E\u003Csup\u003E1\u003C\/sup\u003EDivision of Primary Care and Public Health, Brighton and Sussex Medical School, Falmer, Brighton, UK\u003C\/address\u003E\u003C\/li\u003E\u003Cli class=\u0022aff\u0022\u003E\u003Ca id=\u0022aff-2\u0022 name=\u0022aff-2\u0022\u003E\u003C\/a\u003E\u003Caddress\u003E\u003Csup\u003E2\u003C\/sup\u003EBarts and the London NHS Trust, London, UK\u003C\/address\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Col class=\u0022corresp-list\u0022\u003E\u003Cli class=\u0022corresp\u0022 id=\u0022corresp-1\u0022\u003E\u003Cspan class=\u0022corresp-label\u0022\u003ECorrespondence to\u003C\/span\u003E A Rosemary Tate; \u003Cspan class=\u0022em-link\u0022\u003E\u003Cspan class=\u0022em-addr\u0022\u003Er.tate{at}bsms.ac.uk\u003C\/span\u003E\u003C\/span\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/div\u003E \u003C\/div\u003E\n\n \n \u003C\/div\u003E\n\u003Cdiv class=\u0022panel-separator\u0022\u003E\u003C\/div\u003E\u003Cdiv class=\u0022panel-pane pane-highwire-markup\u0022 \u003E\n \n \n \n \u003Cdiv class=\u0022pane-content\u0022\u003E\n \u003Cdiv class=\u0022highwire-markup\u0022\u003E\u003Cdiv xmlns=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022 id=\u0022content-block\u0022 xmlns:xhtml=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022\u003E\u003Cdiv class=\u0022article abstract-view\u0022\u003E\u003Cspan class=\u0022highwire-journal-article-marker-start\u0022\u003E\u003C\/span\u003E\u003Cdiv class=\u0022section abstract\u0022 id=\u0022abstract-1\u0022\u003E\u003Ch2\u003EAbstract\u003C\/h2\u003E\u003Cdiv id=\u0022sec-1\u0022 class=\u0022subsection\u0022\u003E\u003Cp id=\u0022p-3\u0022\u003E\u003Cstrong\u003EBackground\u003C\/strong\u003E Primary care databases provide a unique resource for healthcare research, but most researchers currently use only the Read codes for their studies, ignoring information in the free text, which is much harder to access.\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv id=\u0022sec-2\u0022 class=\u0022subsection\u0022\u003E\u003Cp id=\u0022p-4\u0022\u003E\u003Cstrong\u003EObjectives\u003C\/strong\u003E To investigate how much information on ovarian cancer diagnosis is \u2018hidden\u2019 in the free text and the time lag between a diagnosis being described in the text or in a hospital letter and the patient being given a Read code for that diagnosis.\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv id=\u0022sec-3\u0022 class=\u0022subsection\u0022\u003E\u003Cp id=\u0022p-5\u0022\u003E\u003Cstrong\u003EDesign\u003C\/strong\u003E Anonymised free text records from the General Practice Research Database of 344 women with a Read code indicating ovarian cancer between 1 June 2002 and 31 May 2007 were used to compare the date at which the diagnosis was first coded with the date at which the diagnosis was recorded in the free text. Free text relating to a diagnosis was identified (\u003Cem\u003Ea\u003C\/em\u003E) from the date of coded diagnosis and (\u003Cem\u003Eb\u003C\/em\u003E) by searching for words relating to the ovary.\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv id=\u0022sec-4\u0022 class=\u0022subsection\u0022\u003E\u003Cp id=\u0022p-6\u0022\u003E\u003Cstrong\u003EResults\u003C\/strong\u003E 90% of cases had information relating to their ovary in the free text. 45% had text indicating a definite diagnosis of ovarian cancer. 22% had text confirming a diagnosis before the coded date; 10% over 4\u2005weeks previously. Four patients did not have ovarian cancer and 10% had only ambiguous or suspected diagnoses associated with the ovarian cancer code.\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv id=\u0022sec-5\u0022 class=\u0022subsection\u0022\u003E\u003Cp id=\u0022p-7\u0022\u003E\u003Cstrong\u003EConclusions\u003C\/strong\u003E There was a vast amount of extra information relating to diagnoses in the free text. Although in most cases text confirmed the coded diagnosis, it also showed that in some cases GPs do not code a definite diagnosis on the date that it is confirmed. For diseases which rely on hospital consultants for diagnosis, free text (particularly letters) is invaluable for accurate dating of diagnosis and referrals and also for identifying misclassified cases.\u003C\/p\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Cul class=\u0022kwd-group\u0022\u003E\u003Cli class=\u0022kwd\u0022\u003EElectronic patient records\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003Esurvey data\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003Enon-response bias in surveys\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003Emultivariate statistics\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003Emisclassification bias\u003C\/li\u003E\u003C\/ul\u003E\u003Cdiv class=\u0022license\u0022 id=\u0022license-1\u0022\u003E\u003Cp id=\u0022p-2\u0022\u003EThis is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: \u003Ca href=\u0022http:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/\u0022\u003Ehttp:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/\u003C\/a\u003E and \u003Ca href=\u0022http:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/legalcode\u0022\u003Ehttp:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/legalcode\u003C\/a\u003E.\u003C\/p\u003E\u003C\/div\u003E\u003Cspan class=\u0022highwire-journal-article-marker-end\u0022\u003E\u003C\/span\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Ca href=\u0022https:\/\/bmjopen.bmj.com\/content\/1\/1\/e000025.full\u0022 class=\u0022hw-link hw-link-article-full-text\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EView Full Text\u003C\/a\u003E\u003C\/div\u003E \u003C\/div\u003E\n\n \n \u003C\/div\u003E\n\u003Cdiv class=\u0022panel-separator\u0022\u003E\u003C\/div\u003E\u003Cdiv class=\u0022panel-pane pane-dfp-pane oas-ads oas-ads-mid pull-right\u0022 \u003E\n \n \n \n \u003Cdiv class=\u0022pane-content\u0022\u003E\n 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class=\u0022pane-title\u0022\u003EStatistics from Altmetric.com\u003C\/h2\u003E\n \n \n \u003Cdiv class=\u0022pane-content\u0022\u003E\n \u003Cdiv data-badge-details=\u0022right\u0022 data-badge-type=\u0022medium-donut\u0022 data-doi=\u002210.1136\/bmjopen-2010-000025\u0022 data-hide-no-mentions=\u0022true\u0022 class=\u0022altmetric-embed\u0022\u003E\u003C\/div\u003E \u003C\/div\u003E\n\n \n \u003C\/div\u003E\n\u003Cdiv class=\u0022panel-separator\u0022\u003E\u003C\/div\u003E\u003Cdiv class=\u0022panel-pane pane-bmjj-jumplinks\u0022 \u003E\n \n \n \n \u003Cdiv class=\u0022pane-content\u0022\u003E\n \u003Cdiv class=\u0022highwire-list-wrapper\u0022\u003E\u003Cdiv class=\u0022highwire-list\u0022\u003E\u003Cul\u003E\u003C\/ul\u003E\u003C\/div\u003E\u003C\/div\u003E \u003C\/div\u003E\n\n \n \u003C\/div\u003E\n\u003Cdiv class=\u0022panel-separator\u0022\u003E\u003C\/div\u003E\u003Cdiv class=\u0022panel-pane pane-highwire-markup\u0022 \u003E\n \n \n \n \u003Cdiv class=\u0022pane-content\u0022\u003E\n \u003Cdiv class=\u0022highwire-markup\u0022\u003E\u003Cdiv xmlns=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022 id=\u0022content-block-markup\u0022 xmlns:xhtml=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022\u003E\u003Cdiv class=\u0022article fulltext-view\u0022\u003E\u003Cspan class=\u0022highwire-journal-article-marker-start\u0022\u003E\u003C\/span\u003E\u003Cul class=\u0022kwd-group\u0022\u003E\u003Cli class=\u0022kwd\u0022\u003E\u003Ca href=\u0022\/keyword\/electronic-patient-records\u0022 class=\u0022hw-term hw-article-keyword hw-article-keyword-electronic-patient-records\u0022 rel=\u0022nofollow\u0022\u003EElectronic patient records\u003C\/a\u003E\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003E\u003Ca href=\u0022\/search\/%20text_abstract_title%3Asurvey%2Bdata%20text_abstract_title_flags%3Amatch-phrase%20sort%3Apublication-date\u0022 class=\u0022hw-term hw-article-keyword hw-article-keyword-survey-data\u0022 rel=\u0022nofollow\u0022\u003Esurvey data\u003C\/a\u003E\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003E\u003Ca href=\u0022\/search\/%20text_abstract_title%3Anon-response%2Bbias%2Bin%2Bsurveys%20text_abstract_title_flags%3Amatch-phrase%20sort%3Apublication-date\u0022 class=\u0022hw-term hw-article-keyword hw-article-keyword-non-response-bias-in-surveys\u0022 rel=\u0022nofollow\u0022\u003Enon-response bias in surveys\u003C\/a\u003E\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003E\u003Ca href=\u0022\/search\/%20text_abstract_title%3Amultivariate%2Bstatistics%20text_abstract_title_flags%3Amatch-phrase%20sort%3Apublication-date\u0022 class=\u0022hw-term hw-article-keyword hw-article-keyword-multivariate-statistics\u0022 rel=\u0022nofollow\u0022\u003Emultivariate statistics\u003C\/a\u003E\u003C\/li\u003E\u003Cli class=\u0022kwd\u0022\u003E\u003Ca href=\u0022\/search\/%20text_abstract_title%3Amisclassification%2Bbias%20text_abstract_title_flags%3Amatch-phrase%20sort%3Apublication-date\u0022 class=\u0022hw-term hw-article-keyword hw-article-keyword-misclassification-bias\u0022 rel=\u0022nofollow\u0022\u003Emisclassification bias\u003C\/a\u003E\u003C\/li\u003E\u003C\/ul\u003E\u003Cdiv class=\u0022boxed-text\u0022 id=\u0022boxed-text-1\u0022\u003E\u003Ch3\u003EArticle summary\u003C\/h3\u003E\u003Cdiv id=\u0022sec-6\u0022 class=\u0022subsection\u0022\u003E\u003Ch4\u003EArticle focus\u003C\/h4\u003E\u003Cul class=\u0022list-unord\u0022 id=\u0022list-1\u0022\u003E\u003Cli id=\u0022list-item-1\u0022\u003E\u003Cp id=\u0022p-8\u0022\u003EHow much information on ovarian cancer diagnoses is \u2018hidden\u2019 in the free text of primary care records?\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-2\u0022\u003E\u003Cp id=\u0022p-9\u0022\u003EHow accurate is the date of diagnosis based only on Read codes?\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-3\u0022\u003E\u003Cp id=\u0022p-10\u0022\u003EHow many cases might be misclassified if codes alone are used to identify diagnoses?\u003C\/p\u003E\u003C\/li\u003E\u003C\/ul\u003E\u003C\/div\u003E\u003Cdiv id=\u0022sec-7\u0022 class=\u0022subsection\u0022\u003E\u003Ch4\u003EKey messages\u003C\/h4\u003E\u003Cul class=\u0022list-unord\u0022 id=\u0022list-2\u0022\u003E\u003Cli id=\u0022list-item-4\u0022\u003E\u003Cp id=\u0022p-11\u0022\u003EFree text contains much extra information on ovarian cancer diagnoses, including the dates on which the patient was investigated and diagnosed in secondary care.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-5\u0022\u003E\u003Cp id=\u0022p-12\u0022\u003EThis information can be used to determine the date at which a diagnosis was notified to the GP and to identify cases that have not been coded.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-6\u0022\u003E\u003Cp id=\u0022p-13\u0022\u003EFor certain disease areas, particularly where specialist care is involved, free text should be used to determine the extent of misclassification associated with both the (coded) date of diagnosis and identification of cases.\u003C\/p\u003E\u003C\/li\u003E\u003C\/ul\u003E\u003C\/div\u003E\u003Cdiv id=\u0022sec-8\u0022 class=\u0022subsection\u0022\u003E\u003Ch4\u003EStrengths and limitations of this study\u003C\/h4\u003E\u003Cul class=\u0022list-unord\u0022 id=\u0022list-3\u0022\u003E\u003Cli id=\u0022list-item-7\u0022\u003E\u003Cp id=\u0022p-14\u0022\u003EAn in-depth analysis of information relating to ovarian cancer diagnoses using free text records from a large primary care database.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-8\u0022\u003E\u003Cp id=\u0022p-15\u0022\u003EWe did not have access to letters that had been scanned in as images, so will have missed some important information.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-9\u0022\u003E\u003Cp id=\u0022p-16\u0022\u003EWe only looked at cases which had been assigned an unambiguous Read code for ovarian cancer and thus will have missed cases with no code or an ambiguous code.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-10\u0022\u003E\u003Cp id=\u0022p-17\u0022\u003EWe ignored text that did not explicitly refer to the patient\u0027s ovaries and thus did not investigate pathways of care or symptoms. This is the topic of a separate study which is already underway.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-11\u0022\u003E\u003Cp id=\u0022p-18\u0022\u003EWe only looked at ovarian cancer, and cannot say whether our findings can be generalised to other diseases.\u003C\/p\u003E\u003C\/li\u003E\u003C\/ul\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Cdiv class=\u0022section intro\u0022 id=\u0022sec-9\u0022\u003E\u003Ch2\u003EIntroduction\u003C\/h2\u003E\u003Cp id=\u0022p-19\u0022\u003EUK primary care databases provide a valuable source of information for research on disease epidemiology, drug safety and adverse drug reactions. The records in these databases contain a mix of coded and free text data. Diseases, symptoms and clinical events are coded using \u2018Read\u2019 codes, enabling searching for clinical entities. Analyses of existing large-scale electronic patient records\u2014most extensively collated in the form of large primary care datasets such as the General Practice Research Database (GPRD), The Health Improvement Network and QResearch\u2014have almost exclusively exploited coded data. Such data are readily accessible to the classical methods of epidemiological analysis, once the complexities of defining and selecting a patient cohort have been overcome.\u003C\/p\u003E\u003Cp id=\u0022p-20\u0022\u003EHowever, since clinicians can choose whether and how to code a consultation, an unknown amount of clinical data is in effect \u2018hidden\u2019 outside the coded data in the free text notes. Free text records, as distinct from coded records, may contain further information on diagnosis (which have been copied or imported from hospital letters) and are also likely to contain important information on the severity of symptoms or on additional symptoms which have not been coded. The degree to which clinical information is coded, and how this varies between by practitioner, practice, or type of clinical problem, is currently unknown. The aim of this study was to determine how much extra information on ovarian cancer diagnosis is recorded in the free text, how often this is recorded before the event date for which the diagnosis is coded and whether information from free text is needed for more accurate dating of diagnosis in research studies.\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv class=\u0022section methods\u0022 id=\u0022sec-10\u0022\u003E\u003Ch2\u003EMethods\u003C\/h2\u003E\u003Cdiv id=\u0022sec-11\u0022 class=\u0022subsection\u0022\u003E\u003Ch3\u003EData\u003C\/h3\u003E\u003Cp id=\u0022p-21\u0022\u003EThis study builds on previous work on dating of diagnosis,\u003Ca id=\u0022xref-ref-1-1\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-1\u0022\u003E1\u003C\/a\u003E where we used coded records from the GPRD; one of the largest primary care databases in the UK. The GPRD contains anonymised longitudinal data on a representative sample of the UK population. Records are being collected on over four million active patients who are registered for care in general practice from around 500 primary care practices throughout the UK. These records are created during consultations or processing correspondence, and are widely used in research on disease epidemiology, drug safety and adverse drug reactions.\u003Ca id=\u0022xref-ref-2-1\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-2\u0022\u003E2\u003C\/a\u003E\u003C\/p\u003E\u003Cp id=\u0022p-22\u0022\u003EThe target population consisted of all women between 40 and 80\u2005years of age (inclusive) who were alive and registered with a GPRD contributing practice on 1 June 2002. From this population, all women with an incident diagnosis of ovarian cancer recorded during 1 June 2002 to 31 May 2007 (ie, with one of the Read codes: B440.00 (malignant neoplasm of ovary), B440.11 (cancer of ovary) or B44.00 (malignant neoplasm of ovary and other uterine adnexa)) were identified (n=1107). From these we chose 374 patients by randomly selecting one-third of the contributing practices. Of these, 344 patients were used for this study after excluding three cases with a previously ambiguous diagnosis before the study period and 27 patients who had been registered with the GP for \u0026lt;2\u2005years before diagnosis. Full details of the sample selection procedures have been provided by Tate \u003Cem\u003Eet al\u003C\/em\u003E.\u003Ca id=\u0022xref-ref-1-2\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-1\u0022\u003E1\u003C\/a\u003E\u003C\/p\u003E\u003Cp id=\u0022p-23\u0022\u003EAt each consultation the GP may enter one or more Read codes into the computer system and, for each code entered, is given the option to add free text which will be associated with that code. Read codes were developed in the 1980s and are currently used for coding clinical events in primary care in the UK. Each code has an associated text description\u2014for example, \u2018abdominal pain\u2019, \u2018ovarian cancer\u2019, \u2018letter from specialist\u2019, which is available on GP systems (usually as a drop down menu) to help them record the correct code. The GP also has the option to enter a date indicating when the event occurred\u2014that is, the \u2018event date\u2019, if this differs from the date of the consultation. In this paper unless otherwise stated \u2018date\u2019 will refer to the event date.\u003C\/p\u003E\u003Cp id=\u0022p-24\u0022\u003EFor our study we obtained anonymised free text records for all consultations recorded during the 12\u2005months before the date of the earliest Read code indicating a referral for, or suspicion of, ovarian cancer (date 4) and up to and including the date of definite diagnosis (date 1), where the dating scheme follows the definitions of our earlier paper\u2014that is,\u003C\/p\u003E\u003Cul class=\u0022list-simple\u0022 id=\u0022list-4\u0022\u003E\u003Cli id=\u0022list-item-12\u0022\u003E\u003Cp id=\u0022p-25\u0022\u003E\u003Cstrong\u003EDate 1. Date of first definite diagnosis\u003C\/strong\u003E\u2014(referred to in this paper as date of coded diagnosis). Earliest recorded (event) date of definite diagnostic code (Read codes as above).\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-13\u0022\u003E\u003Cp id=\u0022p-26\u0022\u003E\u003Cstrong\u003EDate 2. Date of first ambiguous diagnosis\u003C\/strong\u003E\u2014Date 1, or, if present, the first date of an \u2018ambiguous\u2019 code (eg, \u2018cancer\u2019, \u2018carcinomatosis\u2019, with no previous cancer diagnosed in another site) if this occurs before, but within 2\u2005years of, date 1.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-14\u0022\u003E\u003Cp id=\u0022p-27\u0022\u003E\u003Cstrong\u003EDate 3. Date GP first knew, or suspected a diagnosis\u003C\/strong\u003E\u2014Date 2, or, if present, first date of code indicating GP already knew of a cancer diagnosis if this occurs before but within 2\u2005years of date 2 (eg, cancer care review, \u2018chemotherapy\u2019 with no previous cancer diagnosis).\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-15\u0022\u003E\u003Cp id=\u0022p-28\u0022\u003E\u003Cstrong\u003EDate 4. Date of first suspicion of, or first referral for, ovarian cancer\u003C\/strong\u003E\u2014date 3, or, if present, the first date of a code for an investigation or referral to a gynaecologist if this is earlier than but within 12\u2005months of date 3.\u003C\/p\u003E\u003C\/li\u003E\u003C\/ul\u003E\u003Cp id=\u0022p-29\u0022\u003EDates 1 and 4 were different in 73% of the 344 ovarian cancer cases (67% of cases had tests or referrals before the diagnosis date). Full details of the codes which were used to define these dates are given in our earlier paper.\u003Ca id=\u0022xref-ref-1-3\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-1\u0022\u003E1\u003C\/a\u003E\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv id=\u0022sec-12\u0022 class=\u0022subsection\u0022\u003E\u003Ch3\u003EExtraction of information on diagnosis from the free text records\u003C\/h3\u003E\u003Cp id=\u0022p-30\u0022\u003ETo find information on ovarian cancer diagnoses in the free text, all free text records that referred to the ovary were identified by automatically extracting records containing the fragment \u2018ovar\u2019, \u2018 ov\u2019, or \u2018 ov.\u2019 (in either upper or lower case). A manual inspection of the results showed that all the matching strings referred to the ovary except for two referring to the drug \u2018Novartin\u2019. These records were excluded as were six records that referred to a family history of ovarian cancer\u2014that is, in the patient\u0027s mother or sister. Textual data recorded on the date of coded diagnosis (ie, text that was associated with the Read code for ovarian cancer or other Read codes recorded on the same date) were then merged with these records. Textual records, together with their associated Read codes, were grouped chronologically by patient ID and if a number of free text records were available for a patient on the same (event) date these were counted as a single record.\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv id=\u0022sec-13\u0022 class=\u0022subsection\u0022\u003E\u003Ch3\u003EClassification scheme for the free text\u003C\/h3\u003E\u003Cp\u003EThe first 50 text records and their associated Read code descriptions were then examined by a gynaecological oncologist (AGRM). Since the major purpose of this study was to determine how often the GP recorded a definite diagnosis before coding it, we decided to err on the side of caution when classifying cases as \u2018definite\u2019. A scheme for classifying a diagnosis recorded in the text records was developed as follows:\u003C\/p\u003E\u003Col class=\u0022list-ord\u0022 id=\u0022list-5\u0022\u003E\u003Cli id=\u0022list-item-16\u0022\u003E\u003Cp id=\u0022p-32\u0022\u003E\u003Cem\u003EBlank\u003C\/em\u003E: there is no information in the text relating to diagnosis of either a benign or malignant condition, or that ovarian cancer is suspected.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-17\u0022\u003E\u003Cp id=\u0022p-33\u0022\u003E\u003Cem\u003EBenign\u003C\/em\u003E: text indicating definite diagnosis of a benign condition\u2014for example, ovarian (cyst)adenoma.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-18\u0022\u003E\u003Cp id=\u0022p-34\u0022\u003E\u003Cem\u003ESuspected\u003C\/em\u003E: text indicating that ovarian cancer is suspected but with no definite diagnosis yet\u2014for example, \u2018possible\u2019 or \u2018probable\u2019 or \u2018highly likely\u2019. Alternatively, a surgeon\u0027s report (or GP entry relating to the report) may describe, for example, the appearance of ovaries, presence of peritoneal spread, or ascites, which implies suspicion of ovarian cancer. Although surgeons can sometimes be very confident of the diagnosis based on operative appearances, and blood tests\/radiology investigations and state the diagnosis as \u2018ovarian cancer\u2019, we classified text as a suspected cancer if there was no mention of histological or cytological confirmation.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-19\u0022\u003E\u003Cp id=\u0022p-35\u0022\u003E\u003Cem\u003EAmbiguous\u003C\/em\u003E: an ambiguous diagnosis\u2014for example, \u2018tumour\u2019, which might be benign or might be a primary or secondary cancer, or \u2018metastatic cancer\u2019, which might be a primary or secondary ovarian cancer or another type of cancer.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-20\u0022\u003E\u003Cp id=\u0022p-36\u0022\u003E\u003Cem\u003ESecondary\u003C\/em\u003E: where the subject of the text (and Read code) is a documented primary malignancy of non-ovarian origin.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-21\u0022\u003E\u003Cp id=\u0022p-37\u0022\u003E\u003Cem\u003EDefinite\u003C\/em\u003E: text indicating that a diagnosis of ovarian cancer has been confirmed. This confirmation had to have been made by a histological or cytological confirmation of ovarian cancer\u2014for example, after surgery such as laparotomy, or cytology from ascitic fluid drainage. In the cases where the information relating to how the doctor arrived at the diagnosis is not there\u2014for example, simply \u2018ovarian cancer\u2019, we assumed that it had been confirmed appropriately. We included borderline ovarian cancers in this category, although they are classed as semi-malignant.\u003C\/p\u003E\u003C\/li\u003E\u003Cli id=\u0022list-item-22\u0022\u003E\u003Cp id=\u0022p-38\u0022\u003E\u003Cem\u003ENegated\u003C\/em\u003E: text indicating specifically that there is no ovarian cancer (despite the Read code).\u003C\/p\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Cp id=\u0022p-39\u0022\u003EThe full set of selected text records were then inspected and assigned a provisional classification by the first author (ART). These were checked by AGRM who reassigned any that had been incorrectly classified or which were not sufficiently clear cut for a non-specialist to classify. Text that had been recorded on the coded date of diagnosis was double-checked to see whether or not it confirmed the Read code for a diagnosis. Any Read codes for ovarian cancer which had no associated text, or text not relevant to the diagnosis, were assumed to be correct. In addition, each text record was classified as a either a \u2018letter\u2019 or \u2018GP notes\u2019, and if there was information on the stage or grade, this was recorded.\u003C\/p\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Cdiv class=\u0022section results\u0022 id=\u0022sec-14\u0022\u003E\u003Ch2\u003EResults\u003C\/h2\u003E\u003Cp id=\u0022p-40\u0022\u003EThe total number of text records, in the specified time period, was 7860, representing 5777 consultations for 340 of the 344 patients. The median number of text records per patient was 19. Of these, 678 text records (representing 245 patients) were found to contain a reference to the patient\u0027s ovary. When these were merged with text recorded on the same date as the coded diagnosis the number of text records increased to 1007, representing 311 patients. The total number of text records, after combining text recorded on the same event date for each patient (and discarding any \u2018blank\u2019 text recorded on the date of diagnosis) was 706 (for 282 patients), 462 of which were recorded before the date of coded diagnosis (191 patients). The analysis was based on these 706 records.\u003C\/p\u003E\u003Cp id=\u0022p-41\u0022\u003EAfter examining the text records it was clear that information about possible ovarian cancer can be recorded at several different stages of the diagnostic process (\u003Ca id=\u0022xref-table-wrap-1-1\u0022 class=\u0022xref-table\u0022 href=\u0022#T1\u0022\u003Etable 1\u003C\/a\u003E). Approximately 25% of the textual data appeared to be electronic letters. These were much more detailed than the GP notes which were often quite terse with misspellings and abbreviations, as illustrated by some of the examples in \u003Ca id=\u0022xref-table-wrap-1-2\u0022 class=\u0022xref-table\u0022 href=\u0022#T1\u0022\u003Etable 1\u003C\/a\u003E. However, not all the letters were available as electronic text; many of the records with a Read code indicating a letter just reported the result of the letter, and approximately 5% of free texts indicated that a letter was available elsewhere (eg, as a scanned letter on an image viewer).\u003C\/p\u003E\u003Cdiv class=\u0022table\u0022 id=\u0022T1\u0022\u003E\u003Cdiv class=\u0022table-inline table-callout-links\u0022\u003E\u003Cdiv class=\u0022callout\u0022\u003E\u003Cspan\u003EView this table:\u003C\/span\u003E\u003Cul class=\u0022callout-links\u0022\u003E\u003Cli class=\u0022view-inline first\u0022\u003E\u003Ca href=\u0022##\u0022 class=\u0022table-expand-inline\u0022 data-table-url=\u0022\/highwire\/markup\/76306\/expansion?postprocessors=highwire_tables%2Chighwire_reclass%2Chighwire_figures%2Chighwire_math%2Chighwire_inline_linked_media%2Chighwire_embed\u0026amp;table-expand-inline=1\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EView inline\u003C\/a\u003E\u003C\/li\u003E\n\u003Cli class=\u0022view-popup last\u0022\u003E\u003Ca href=\u0022\/highwire\/markup\/76306\/expansion?width=1000\u0026amp;height=500\u0026amp;iframe=true\u0026amp;postprocessors=highwire_tables%2Chighwire_reclass%2Chighwire_figures%2Chighwire_math%2Chighwire_inline_linked_media%2Chighwire_embed\u0022 class=\u0022colorbox colorbox-load table-expand-popup\u0022 rel=\u0022gallery-fragment-tables\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EView popup\u003C\/a\u003E\u003C\/li\u003E\n\u003C\/ul\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Cdiv class=\u0022table-caption\u0022\u003E\u003Cspan class=\u0022table-label\u0022\u003ETable 1\u003C\/span\u003E \u003Cp id=\u0022p-42\u0022 class=\u0022first-child\u0022\u003ETypical situations and use of text to describe the diagnostic process for patients with ovarian cancer and number of free texts and patients with text (referring to the ovary) according to our classification scheme\u003C\/p\u003E\u003Cdiv class=\u0022sb-div caption-clear\u0022\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Cp id=\u0022p-45\u0022\u003EAccording to our classification scheme, 64% of patients had text either recording or confirming a definite diagnosis and 32% had a \u2018probable\u2019 or \u2018ambiguous\u2019 diagnosis. \u003Ca id=\u0022xref-fig-1-1\u0022 class=\u0022xref-fig\u0022 href=\u0022#F1\u0022\u003EFigure 1\u003C\/a\u003E depicts the text classifications in relation to the coded date of diagnosis.\u003C\/p\u003E\u003Cdiv id=\u0022F1\u0022 class=\u0022fig odd\u0022\u003E\u003Cdiv class=\u0022highwire-figure\u0022\u003E\u003Cdiv class=\u0022fig-inline-img-wrapper\u0022\u003E\u003Cdiv class=\u0022fig-inline-img\u0022\u003E\u003Ca href=\u0022https:\/\/bmjopen.bmj.com\/content\/bmjopen\/1\/1\/e000025\/F1.large.jpg?width=800\u0026amp;height=600\u0026amp;carousel=1\u0022 title=\u0022Number of patients and text classifications with event dates on and prior to the coded date of diagnosis.\u0022 class=\u0022highwire-fragment fragment-images colorbox-load\u0022 rel=\u0022gallery-fragment-images-1123918673\u0022 data-figure-caption=\u0022\u0026lt;div class=\u0026quot;highwire-markup\u0026quot;\u0026gt;Number of patients and text classifications with event dates on and prior to the coded date of diagnosis.\u0026lt;\/div\u0026gt;\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003E\u003Cspan class=\u0022hw-responsive-img\u0022\u003E\u003Cimg class=\u0022highwire-fragment fragment-image lazyload\u0022 alt=\u0022Figure 1\u0022 src=\u0022data:image\/gif;base64,R0lGODlhAQABAIAAAAAAAP\/\/\/yH5BAEAAAAALAAAAAABAAEAAAIBRAA7\u0022 data-src=\u0022https:\/\/bmjopen.bmj.com\/content\/bmjopen\/1\/1\/e000025\/F1.medium.gif\u0022\/\u003E\u003Cnoscript\u003E\u003Cimg class=\u0022highwire-fragment fragment-image\u0022 alt=\u0022Figure 1\u0022 src=\u0022https:\/\/bmjopen.bmj.com\/content\/bmjopen\/1\/1\/e000025\/F1.medium.gif\u0022\/\u003E\u003C\/noscript\u003E\u003C\/span\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Cul class=\u0022highwire-figure-links inline\u0022\u003E\u003Cli class=\u0022download-fig first\u0022\u003E\u003Ca href=\u0022https:\/\/bmjopen.bmj.com\/content\/bmjopen\/1\/1\/e000025\/F1.large.jpg?download=true\u0022 class=\u0022highwire-figure-link highwire-figure-link-download\u0022 title=\u0022Download Figure 1\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EDownload figure\u003C\/a\u003E\u003C\/li\u003E\n\u003Cli class=\u0022new-tab\u0022\u003E\u003Ca href=\u0022https:\/\/bmjopen.bmj.com\/content\/bmjopen\/1\/1\/e000025\/F1.large.jpg\u0022 class=\u0022highwire-figure-link highwire-figure-link-newtab\u0022 target=\u0022_blank\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EOpen in new tab\u003C\/a\u003E\u003C\/li\u003E\n\u003Cli class=\u0022download-ppt last\u0022\u003E\u003Ca href=\u0022\/highwire\/powerpoint\/76124\u0022 class=\u0022highwire-figure-link highwire-figure-link-ppt\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EDownload powerpoint\u003C\/a\u003E\u003C\/li\u003E\n\u003C\/ul\u003E\u003C\/div\u003E\u003Cdiv class=\u0022fig-caption\u0022 xmlns:xhtml=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022\u003E\u003Cspan class=\u0022fig-label\u0022\u003EFigure 1\u003C\/span\u003E \u003Cp id=\u0022p-46\u0022 class=\u0022first-child\u0022\u003ENumber of patients and text classifications with event dates on and prior to the coded date of diagnosis.\u003C\/p\u003E\u003Cdiv class=\u0022sb-div caption-clear\u0022\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Cdiv id=\u0022sec-15\u0022 class=\u0022subsection\u0022\u003E\u003Ch3\u003EText classified as \u2018definite\u2019\u003C\/h3\u003E\u003Cp id=\u0022p-47\u0022\u003EThe majority of text records that were classified as definite were recorded on the same date as the patient\u0027s first ovarian cancer code (205 (60%) patients). However 74 (22%) patients had a \u2018definite\u2019 diagnosis recorded in the text before this date. The median (IQR) difference between the date that the diagnosis was coded and the date of the text for these 74 patients was 24 (8,67) days, with 34 (10%) of patients having a diagnosis more than 4\u2005weeks before. Six patients had text stating that they had a recurrence of previously diagnosed ovarian cancer. All six of these had a previous definite diagnosis in the free text and one had a previous ambiguous code \u2018carcinoma in situ of the ovary\u2019, a year earlier.\u003C\/p\u003E\u003Cp id=\u0022p-48\u0022\u003EFourteen patients were classified as definite before the derived date of first suspicion or investigation for ovarian cancer (date 4), 10 when this differed from date 1, but only four of these (of which three were described in the text as a recurrent case) had a diagnosis in the text more than 4\u2005weeks before date 4.\u003C\/p\u003E\u003Cp id=\u0022p-49\u0022\u003EApproximately two-thirds of the texts indicating a definite diagnosis had been entered in association with a Read code that was not ovarian cancer (including 55 texts recorded on date 1). Approximately one-third of these had a code indicating a visit to an oncologist or gynaecologist or a \u2018letter from specialist\u2019 or similar. The other third were associated with a variety of different codes\u2014for example, a code for an operation or hospital discharge letter, a generic cancer code (eg, \u2018adenocarcinomas\u2019) or a code which bore no relation to the diagnosis at all\u2014for example \u2018excepted from diabetes quality indicators\u2019 (four patients), \u2018fracture of neck of femur\u2019 (one patient).\u003C\/p\u003E\u003Cp id=\u0022p-50\u0022\u003ETwenty-eight per cent of patients had information on the stage, grade or spread of the tumour.\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv id=\u0022sec-16\u0022 class=\u0022subsection\u0022\u003E\u003Ch3\u003EOther classifications\u003C\/h3\u003E\u003Cp id=\u0022p-51\u0022\u003EThirty-nine patients (11%) were classified as not having a definite diagnosis of ovarian cancer on or before the date of coded diagnosis (\u003Ca id=\u0022xref-fig-1-2\u0022 class=\u0022xref-fig\u0022 href=\u0022#F1\u0022\u003Efigure 1\u003C\/a\u003E). The text records of four patients indicated that there was definitely no ovarian cancer: one had a metastasis in the breast, two a cancer in another site and one was worried she might have cancer, but subsequent coded records for this patient showed no further indication of cancer, so we assumed this had been coded in error. The other 35 patients had only a suspected or ambiguous diagnosis. Examination of subsequent codes for these patients indicated that all these patients did indeed have cancer (19 died or went into a hospice, 15 had a subsequent (repeated) code for ovarian cancer and most had codes for chemotherapy or cancer care).\u003C\/p\u003E\u003Cp id=\u0022p-52\u0022\u003EThirty-one patients had an ambiguous, or suspected diagnosis before date 4 (17 where date 1 and date 4 were different); the median (IQR) difference was 13 (6, 25) days, with five (3 where date 1 and date 4 were different) patients having this classification more than 4\u2005weeks previously.\u003C\/p\u003E\u003C\/div\u003E\u003C\/div\u003E\u003Cdiv class=\u0022section discussion\u0022 id=\u0022sec-17\u0022\u003E\u003Ch2\u003EDiscussion\u003C\/h2\u003E\u003Cp id=\u0022p-53\u0022\u003EThis analysis shows that primary care records hold a large amount of free text containing information on ovarian cancer diagnoses. The majority (90%) of the 344 patients had free text relating to their ovarian pathology and 64% had free text confirming an ovarian cancer code. However, the information in the text was not always reflected in the codes. In some cases a \u2018definite diagnosis\u2019 in the text field preceded the coded diagnosis, with 22% of patients having a \u2018definite\u2019 classification of ovarian cancer recorded in the text before the date of the first ovarian cancer code. Half of these cases had a \u2018definite\u2019 classification more than 24\u2005days before the coded date. However, only 10 of these diagnoses occurred before our derived date for suspicion of, or referral for, ovarian cancer. A number of other inconsistencies were identified using the free text: four patients did not have ovarian cancer at all and six were recurrences of a much earlier ovarian cancer not evident from the codes.\u003C\/p\u003E\u003Cp id=\u0022p-54\u0022\u003EThe delay between the GP recording the diagnosis in the text and coding might be explained partly by incorrect entry of dates or by the administrative practices of the surgery. For example, practice staff code and date the letters when they arrive and the GPs assigns the cancer code at a later date. This latter supposition was supported by the fact that approximately 50% of \u2018definite\u2019 classifications recorded before the coded date came from the text of letters (as opposed to about 25% recorded on the date of diagnosis).\u003C\/p\u003E\u003Cp id=\u0022p-55\u0022\u003EThere is no Read code for a possible, probable or highly likely diagnosis, and this may explain why 10% of the patients classified as having only a suspected or ambiguous diagnosis nevertheless had an ovarian cancer code. Conversely, \u2018definite\u2019 diagnoses in free text were often associated with a very general Read code (eg, \u2018letter from specialist\u2019). Since most studies of diseases are based on the codes, wrongly or uncoded cases will lead to incorrect estimates of the incidence of the disease and will also have an impact on case selection. In addition, incorrectly entered dates of the notification of diagnosis will have an impact on the findings of studies on the incidence of symptoms and delay before diagnosis. How much difference this will make will depend on the disease and also on the time period used for calculating incidence. For this dataset, redefining the (coded) date of diagnosis using the free text did not have much effect on estimates of delay or incidence of symptoms (data not shown), but this might not be the case for other diseases.\u003C\/p\u003E\u003Cp id=\u0022p-56\u0022\u003ETo our knowledge this is the only work which explicitly explores and reports dating of diagnoses in GP records using the textual part of the record. Other studies creatively used code lists\u2014for example, our previous study,\u003Ca id=\u0022xref-ref-1-4\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-1\u0022\u003E1\u003C\/a\u003E or GP questionnaires\u2014for example, the study of Hammad \u003Cem\u003Eet al\u003C\/em\u003E,\u003Ca id=\u0022xref-ref-3-1\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-3\u0022\u003E3\u003C\/a\u003E to investigate the accuracy of the coded date. A handful of studies have used free text to verify clinical conditions in combination with codes; a few of them have used free text to identify cases\u003Ca id=\u0022xref-ref-4-1\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-4\u0022\u003E4\u003C\/a\u003E \u003Ca id=\u0022xref-ref-5-1\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-5\u0022\u003E5\u003C\/a\u003E while the majority have used free text to verify and validate coded information.\u003Ca id=\u0022xref-ref-3-2\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-3\u0022\u003E3\u003C\/a\u003E \u003Ca id=\u0022xref-ref-6-1\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-6\u0022\u003E6\u20139\u003C\/a\u003E However, with the exception of the study by Wurst \u003Cem\u003Eet al\u003C\/em\u003E,\u003Ca id=\u0022xref-ref-7-1\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-7\u0022\u003E7\u003C\/a\u003E most studies have little or no detail on the process of selection and review of the free text that was used.\u003C\/p\u003E\u003Cp id=\u0022p-57\u0022\u003EIn this study we looked only at cases that had an unambiguous diagnosis code for ovarian cancer, so we will have missed any that had not been coded or which had ambiguous codes. Our recent comparison with the cancer registries\u003Ca id=\u0022xref-ref-10-1\u0022 class=\u0022xref-bibr\u0022 href=\u0022#ref-10\u0022\u003E10\u003C\/a\u003E indicated that around 9% of cases may not have been coded and thus missed in this way. Another limitation was that we did not have access to letters that were not available in electronic text format, which might have contained important information that was not relayed by the GP. We estimate (data not shown) that approximately 20\u201325% of hospital letters for these patients will not have any information on their content (either a code or text) entered on the date that they were received. It is likely that many of these letters will contain information on diagnosis, particularly for cancer, where a specialist will always make the diagnosis. However, with the increased transfer of electronic records and even sharing of hospital records this problem is likely to be resolved in the near future.\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv class=\u0022section conclusions\u0022 id=\u0022sec-18\u0022\u003E\u003Ch2\u003EConclusions\u003C\/h2\u003E\u003Cp id=\u0022p-58\u0022\u003EThis study gives an in-depth insight into the extra information that is contained in the free text part of records relating to a suspected or confirmed diagnosis of ovarian cancer. A large amount of information in free text is available that modifies the coded date or discloses incorrect classification as a case, even for \u2018hard\u2019 outcomes such as ovarian cancer, which is considered well documented in primary care records. This shows that (\u003Cem\u003Ea\u003C\/em\u003E) the quality of information in primary care records is better than one might think, but (\u003Cem\u003Eb\u003C\/em\u003E) free text needs to be routinely explored to take advantage of this quality information. It is likely that the proportion of information concealed in free text will be greater for less \u2018hard\u2019 outcomes in certain disease areas. We are therefore working with natural language processing experts to find ways of extracting relevant information automatically (and therefore more cost effectively) from large volumes of text.\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv class=\u0022section ack\u0022 id=\u0022ack-1\u0022\u003E\u003Ch2\u003EAcknowledgments\u003C\/h2\u003E\u003Cp id=\u0022p-59\u0022\u003EWe thank the PREP team and John Parkinson for helpful comments and discussions.\u003C\/p\u003E\u003C\/div\u003E\u003Cdiv class=\u0022section ref-list\u0022 id=\u0022ref-list-1\u0022\u003E\u003Ch2\u003EReferences\u003C\/h2\u003E\u003Col class=\u0022cit-list\u0022\u003E\u003Cli\u003E\u003Ca class=\u0022rev-xref-ref\u0022 href=\u0022#xref-ref-1-1\u0022 title=\u0022View reference 1 in text\u0022 id=\u0022ref-1\u0022\u003E\u21b5\u003C\/a\u003E\u003Cdiv class=\u0022cit ref-cit ref-journal\u0022 id=\u0022cit-1.1.e000025.1\u0022 data-doi=\u002210.1186\/1471-2288-9-42\u0022\u003E\u003Cdiv class=\u0022cit-metadata\u0022\u003E\u003Col class=\u0022cit-auth-list\u0022\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003ETate\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EAR\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EMartin\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EAG\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EMurray-Thomas\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003ET\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-etal\u0022\u003Eet al\u003C\/span\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Ccite\u003E. \u003Cspan class=\u0022cit-article-title\u0022\u003EDetermining the date of diagnosis\u2014is it a simple matter? The impact of different approaches to dating diagnosis on estimates of delayed care for ovarian cancer in UK primary care\u003C\/span\u003E. \u003Cabbr class=\u0022cit-jnl-abbrev\u0022\u003EBMC Med Res Methodol\u003C\/abbr\u003E \u003Cspan class=\u0022cit-pub-date\u0022\u003E2009\u003C\/span\u003E;\u003Cspan class=\u0022cit-vol\u0022\u003E9\u003C\/span\u003E:\u003Cspan class=\u0022cit-fpage\u0022\u003E42\u003C\/span\u003E.\u003C\/cite\u003E\u003C\/div\u003E\u003Cdiv class=\u0022cit-extra\u0022\u003E\u003Ca href=\u0022{openurl}?query=rft.jtitle%253DBMC%2Bmedical%2Bresearch%2Bmethodology%2B%255Belectronic%2Bresource%255D%26rft.stitle%253DBMC%2BMed%2BRes%2BMethodol%26rft.aulast%253DTate%26rft.auinit1%253DA.%2BR.%26rft.volume%253D9%26rft.spage%253D42%26rft.epage%253D42%26rft.atitle%253DDetermining%2Bthe%2Bdate%2Bof%2Bdiagnosis--is%2Bit%2Ba%2Bsimple%2Bmatter%253F%2BThe%2Bimpact%2Bof%2Bdifferent%2Bapproaches%2Bto%2Bdating%2Bdiagnosis%2Bon%2Bestimates%2Bof%2Bdelayed%2Bcare%2Bfor%2Bovarian%2Bcancer%2Bin%2BUK%2Bprimary%2Bcare.%26rft_id%253Dinfo%253Adoi%252F10.1186%252F1471-2288-9-42%26rft_id%253Dinfo%253Apmid%252F19549322%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-openurl cit-ref-sprinkles-open-url\u0022\u003E\u003Cspan\u003EOpenUrl\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=10.1186\/1471-2288-9-42\u0026amp;link_type=DOI\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-doi cit-ref-sprinkles-crossref\u0022\u003E\u003Cspan\u003ECrossRef\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=19549322\u0026amp;link_type=MED\u0026amp;atom=%2Fbmjopen%2F1%2F1%2Fe000025.atom\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-medline\u0022\u003E\u003Cspan\u003EPubMed\u003C\/span\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\u003Cli\u003E\u003Ca class=\u0022rev-xref-ref\u0022 href=\u0022#xref-ref-2-1\u0022 title=\u0022View reference 2 in text\u0022 id=\u0022ref-2\u0022\u003E\u21b5\u003C\/a\u003E\u003Cdiv class=\u0022cit ref-cit ref-other\u0022 id=\u0022cit-1.1.e000025.2\u0022\u003E\u003Cdiv class=\u0022cit-metadata\u0022\u003E\u003Ccite\u003E\u003Cspan class=\u0022cit-auth cit-collab\u0022\u003EGPRD\u003C\/span\u003E. \u003Cspan class=\u0022cit-article-title\u0022\u003EExcellence in public health research\u003C\/span\u003E. \u003Cspan class=\u0022cit-pub-date\u0022\u003E2010\u003C\/span\u003E. \u003Ca href=\u0022http:\/\/www.gprd.com\u0022\u003Ehttp:\/\/www.gprd.com\u003C\/a\u003E.\u003C\/cite\u003E\u003C\/div\u003E\u003Cdiv class=\u0022cit-extra\u0022\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\u003Cli\u003E\u003Ca class=\u0022rev-xref-ref\u0022 href=\u0022#xref-ref-3-1\u0022 title=\u0022View reference 3 in text\u0022 id=\u0022ref-3\u0022\u003E\u21b5\u003C\/a\u003E\u003Cdiv class=\u0022cit ref-cit ref-journal\u0022 id=\u0022cit-1.1.e000025.3\u0022 data-doi=\u002210.1002\/pds.1672\u0022\u003E\u003Cdiv class=\u0022cit-metadata\u0022\u003E\u003Col class=\u0022cit-auth-list\u0022\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EHammad\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003ETA\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EMcAdams\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EMA\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EFeight\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EA\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-etal\u0022\u003Eet al\u003C\/span\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Ccite\u003E. \u003Cspan class=\u0022cit-article-title\u0022\u003EDetermining the predictive value of Read\/OXMIS codes to identify incident acute myocardial infarction in the General Practice Research Database\u003C\/span\u003E. \u003Cabbr class=\u0022cit-jnl-abbrev\u0022\u003EPharmacoepidemiol Drug Saf\u003C\/abbr\u003E \u003Cspan class=\u0022cit-pub-date\u0022\u003E2008\u003C\/span\u003E;\u003Cspan class=\u0022cit-vol\u0022\u003E17\u003C\/span\u003E:\u003Cspan class=\u0022cit-fpage\u0022\u003E1197\u003C\/span\u003E\u2013\u003Cspan class=\u0022cit-lpage\u0022\u003E201\u003C\/span\u003E.\u003C\/cite\u003E\u003C\/div\u003E\u003Cdiv class=\u0022cit-extra\u0022\u003E\u003Ca href=\u0022{openurl}?query=rft.jtitle%253DPharmacoepidemiology%2Band%2Bdrug%2Bsafety%26rft.stitle%253DPharmacoepidemiol%2BDrug%2BSaf%26rft.aulast%253DHammad%26rft.auinit1%253DT.%2BA.%26rft.volume%253D17%26rft.issue%253D12%26rft.spage%253D1197%26rft.epage%253D1201%26rft.atitle%253DDetermining%2Bthe%2Bpredictive%2Bvalue%2Bof%2BRead%252FOXMIS%2Bcodes%2Bto%2Bidentify%2Bincident%2Bacute%2Bmyocardial%2Binfarction%2Bin%2Bthe%2BGeneral%2BPractice%2BResearch%2BDatabase.%26rft_id%253Dinfo%253Adoi%252F10.1002%252Fpds.1672%26rft_id%253Dinfo%253Apmid%252F18985705%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-openurl cit-ref-sprinkles-open-url\u0022\u003E\u003Cspan\u003EOpenUrl\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=10.1002\/pds.1672\u0026amp;link_type=DOI\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-doi cit-ref-sprinkles-crossref\u0022\u003E\u003Cspan\u003ECrossRef\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=18985705\u0026amp;link_type=MED\u0026amp;atom=%2Fbmjopen%2F1%2F1%2Fe000025.atom\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-medline\u0022\u003E\u003Cspan\u003EPubMed\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=000261912200009\u0026amp;link_type=ISI\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-newisilink cit-ref-sprinkles-webofscience\u0022\u003E\u003Cspan\u003EWeb of Science\u003C\/span\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\u003Cli\u003E\u003Ca class=\u0022rev-xref-ref\u0022 href=\u0022#xref-ref-4-1\u0022 title=\u0022View reference 4 in text\u0022 id=\u0022ref-4\u0022\u003E\u21b5\u003C\/a\u003E\u003Cdiv class=\u0022cit ref-cit ref-journal\u0022 id=\u0022cit-1.1.e000025.4\u0022 data-doi=\u002210.1136\/jech.2008.080382\u0022\u003E\u003Cdiv class=\u0022cit-metadata\u0022\u003E\u003Col class=\u0022cit-auth-list\u0022\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EMasso Gonzalez\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EEL\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EJohansson\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003ES\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EWallander\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EMA\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-etal\u0022\u003Eet al\u003C\/span\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Ccite\u003E. \u003Cspan class=\u0022cit-article-title\u0022\u003ETrends in the prevalence and incidence of diabetes in the UK: 1996\u20132005\u003C\/span\u003E. \u003Cabbr class=\u0022cit-jnl-abbrev\u0022\u003EJ Epidemiol Community Health\u003C\/abbr\u003E \u003Cspan class=\u0022cit-pub-date\u0022\u003E2009\u003C\/span\u003E;\u003Cspan class=\u0022cit-vol\u0022\u003E63\u003C\/span\u003E:\u003Cspan class=\u0022cit-fpage\u0022\u003E332\u003C\/span\u003E\u2013\u003Cspan class=\u0022cit-lpage\u0022\u003E6\u003C\/span\u003E.\u003C\/cite\u003E\u003C\/div\u003E\u003Cdiv class=\u0022cit-extra\u0022\u003E\u003Ca href=\u0022{openurl}?query=rft.jtitle%253DJ%2BEpidemiol%2BCommunity%2BHealth%26rft_id%253Dinfo%253Adoi%252F10.1136%252Fjech.2008.080382%26rft_id%253Dinfo%253Apmid%252F19240084%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-openurl cit-ref-sprinkles-open-url\u0022\u003E\u003Cspan\u003EOpenUrl\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/ijlink\/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiamVjaCI7czo1OiJyZXNpZCI7czo4OiI2My80LzMzMiI7czo0OiJhdG9tIjtzOjI1OiIvYm1qb3Blbi8xLzEvZTAwMDAyNS5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30=\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-ijlink\u0022\u003E\u003Cspan\u003E\u003Cspan class=\u0022cit-reflinks-abstract\u0022\u003EAbstract\u003C\/span\u003E\u003Cspan class=\u0022cit-sep cit-reflinks-variant-name-sep\u0022\u003E\/\u003C\/span\u003E\u003Cspan class=\u0022cit-reflinks-full-text\u0022\u003E\u003Cspan class=\u0022free-full-text\u0022\u003EFREE \u003C\/span\u003EFull Text\u003C\/span\u003E\u003C\/span\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\u003Cli\u003E\u003Ca class=\u0022rev-xref-ref\u0022 href=\u0022#xref-ref-5-1\u0022 title=\u0022View reference 5 in text\u0022 id=\u0022ref-5\u0022\u003E\u21b5\u003C\/a\u003E\u003Cdiv class=\u0022cit ref-cit ref-journal\u0022 id=\u0022cit-1.1.e000025.5\u0022 data-doi=\u002210.1136\/bmj.c249\u0022\u003E\u003Cdiv class=\u0022cit-metadata\u0022\u003E\u003Col class=\u0022cit-auth-list\u0022\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EMartinez\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EC\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EAssimes\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003ETL\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EMines\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003ED\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-etal\u0022\u003Eet al\u003C\/span\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Ccite\u003E. \u003Cspan class=\u0022cit-article-title\u0022\u003EUse of venlafaxine compared with other antidepressants and the risk of sudden cardiac death or near death: a nested case-control study\u003C\/span\u003E. \u003Cabbr class=\u0022cit-jnl-abbrev\u0022\u003EBMJ\u003C\/abbr\u003E \u003Cspan class=\u0022cit-pub-date\u0022\u003E2010\u003C\/span\u003E;\u003Cspan class=\u0022cit-vol\u0022\u003E340\u003C\/span\u003E:\u003Cspan class=\u0022cit-fpage\u0022\u003Ec249\u003C\/span\u003E.\u003C\/cite\u003E\u003C\/div\u003E\u003Cdiv class=\u0022cit-extra\u0022\u003E\u003Ca href=\u0022{openurl}?query=rft.jtitle%253DBMJ%26rft_id%253Dinfo%253Adoi%252F10.1136%252Fbmj.c249%26rft_id%253Dinfo%253Apmid%252F20139216%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-openurl cit-ref-sprinkles-open-url\u0022\u003E\u003Cspan\u003EOpenUrl\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/ijlink\/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6MzoiYm1qIjtzOjU6InJlc2lkIjtzOjE2OiIzNDAvZmViMDVfMS9jMjQ5IjtzOjQ6ImF0b20iO3M6MjU6Ii9ibWpvcGVuLzEvMS9lMDAwMDI1LmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-ijlink\u0022\u003E\u003Cspan\u003E\u003Cspan class=\u0022cit-reflinks-abstract\u0022\u003EAbstract\u003C\/span\u003E\u003Cspan class=\u0022cit-sep cit-reflinks-variant-name-sep\u0022\u003E\/\u003C\/span\u003E\u003Cspan class=\u0022cit-reflinks-full-text\u0022\u003E\u003Cspan class=\u0022free-full-text\u0022\u003EFREE \u003C\/span\u003EFull Text\u003C\/span\u003E\u003C\/span\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\u003Cli\u003E\u003Ca class=\u0022rev-xref-ref\u0022 href=\u0022#xref-ref-6-1\u0022 title=\u0022View reference 6 in text\u0022 id=\u0022ref-6\u0022\u003E\u21b5\u003C\/a\u003E\u003Cdiv class=\u0022cit ref-cit ref-journal\u0022 id=\u0022cit-1.1.e000025.6\u0022 data-doi=\u002210.1093\/aje\/kwn310\u0022\u003E\u003Cdiv class=\u0022cit-metadata\u0022\u003E\u003Col class=\u0022cit-auth-list\u0022\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EStowe\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EJ\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EAndrews\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EN\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EWise\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EL\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-etal\u0022\u003Eet al\u003C\/span\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Ccite\u003E. \u003Cspan class=\u0022cit-article-title\u0022\u003EInvestigation of the temporal association of Guillain-Barre syndrome with inuenza vaccine and inuenzalike illness using the United Kingdom General Practice Research Database\u003C\/span\u003E. \u003Cabbr class=\u0022cit-jnl-abbrev\u0022\u003EAm J Epidemiol\u003C\/abbr\u003E \u003Cspan class=\u0022cit-pub-date\u0022\u003E2009\u003C\/span\u003E;\u003Cspan class=\u0022cit-vol\u0022\u003E169\u003C\/span\u003E:\u003Cspan class=\u0022cit-fpage\u0022\u003E382\u003C\/span\u003E\u2013\u003Cspan class=\u0022cit-lpage\u0022\u003E8\u003C\/span\u003E.\u003C\/cite\u003E\u003C\/div\u003E\u003Cdiv class=\u0022cit-extra\u0022\u003E\u003Ca href=\u0022{openurl}?query=rft.jtitle%253DAm%2BJ%2BEpidemiol%26rft_id%253Dinfo%253Adoi%252F10.1093%252Faje%252Fkwn310%26rft_id%253Dinfo%253Apmid%252F19033158%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-openurl cit-ref-sprinkles-open-url\u0022\u003E\u003Cspan\u003EOpenUrl\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/ijlink\/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NzoiYW1qZXBpZCI7czo1OiJyZXNpZCI7czo5OiIxNjkvMy8zODIiO3M6NDoiYXRvbSI7czoyNToiL2Jtam9wZW4vMS8xL2UwMDAwMjUuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-ijlink\u0022\u003E\u003Cspan\u003E\u003Cspan class=\u0022cit-reflinks-abstract\u0022\u003EAbstract\u003C\/span\u003E\u003Cspan class=\u0022cit-sep cit-reflinks-variant-name-sep\u0022\u003E\/\u003C\/span\u003E\u003Cspan class=\u0022cit-reflinks-full-text\u0022\u003E\u003Cspan class=\u0022free-full-text\u0022\u003EFREE \u003C\/span\u003EFull Text\u003C\/span\u003E\u003C\/span\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\u003Cli\u003E\u003Ca class=\u0022rev-xref-ref\u0022 href=\u0022#xref-ref-6-1\u0022 title=\u0022View reference 7 in text\u0022 id=\u0022ref-7\u0022\u003E\u21b5\u003C\/a\u003E\u003Cdiv class=\u0022cit ref-cit ref-journal\u0022 id=\u0022cit-1.1.e000025.7\u0022\u003E\u003Cdiv class=\u0022cit-metadata\u0022\u003E\u003Col class=\u0022cit-auth-list\u0022\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EWurst\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EKE\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EEphross\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003ESA\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003ELoehr\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EJ\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-etal\u0022\u003Eet al\u003C\/span\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Ccite\u003E. \u003Cspan class=\u0022cit-article-title\u0022\u003EThe utility of the general practice research database to examine selected congenital heart defects: a validation study\u003C\/span\u003E. \u003Cabbr class=\u0022cit-jnl-abbrev\u0022\u003EPharmacoepidemiol Drug Saf\u003C\/abbr\u003E \u003Cspan class=\u0022cit-pub-date\u0022\u003E2007\u003C\/span\u003E;\u003Cspan class=\u0022cit-vol\u0022\u003E16\u003C\/span\u003E:\u003Cspan class=\u0022cit-fpage\u0022\u003E867\u003C\/span\u003E\u2013\u003Cspan class=\u0022cit-lpage\u0022\u003E77\u003C\/span\u003E.\u003C\/cite\u003E\u003C\/div\u003E\u003Cdiv class=\u0022cit-extra\u0022\u003E\u003Ca href=\u0022{openurl}?query=rft.jtitle%253DPharmacoepidemiology%2Band%2Bdrug%2Bsafety%26rft.stitle%253DPharmacoepidemiol%2BDrug%2BSaf%26rft.aulast%253DWurst%26rft.auinit1%253DK.%2BE.%26rft.volume%253D16%26rft.issue%253D8%26rft.spage%253D867%26rft.epage%253D877%26rft.atitle%253DThe%2Butility%2Bof%2Bthe%2Bgeneral%2Bpractice%2Bresearch%2Bdatabase%2Bto%2Bexamine%2Bselected%2Bcongenital%2Bheart%2Bdefects%253A%2Ba%2Bvalidation%2Bstudy.%26rft_id%253Dinfo%253Apmid%252F17563909%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-openurl cit-ref-sprinkles-open-url\u0022\u003E\u003Cspan\u003EOpenUrl\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=17563909\u0026amp;link_type=MED\u0026amp;atom=%2Fbmjopen%2F1%2F1%2Fe000025.atom\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-medline\u0022\u003E\u003Cspan\u003EPubMed\u003C\/span\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\u003Cli\u003E\u003Ca class=\u0022rev-xref-ref\u0022 href=\u0022#xref-ref-6-1\u0022 title=\u0022View reference 8 in text\u0022 id=\u0022ref-8\u0022\u003E\u21b5\u003C\/a\u003E\u003Cdiv class=\u0022cit ref-cit ref-journal\u0022 id=\u0022cit-1.1.e000025.8\u0022 data-doi=\u002210.1002\/pds.1919\u0022\u003E\u003Cdiv class=\u0022cit-metadata\u0022\u003E\u003Col class=\u0022cit-auth-list\u0022\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003ERuigomez\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EA\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EMartin-Merino\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EE\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EGarcia Rodriguez\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003ELA\u003C\/span\u003E\u003C\/span\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Ccite\u003E. \u003Cspan class=\u0022cit-article-title\u0022\u003EValidation of ischemic cere-brovascular diagnoses in the health improvement network (THIN)\u003C\/span\u003E. \u003Cabbr class=\u0022cit-jnl-abbrev\u0022\u003EPharmacoepidemiol Drug Saf\u003C\/abbr\u003E \u003Cspan class=\u0022cit-pub-date\u0022\u003E2010\u003C\/span\u003E;\u003Cspan class=\u0022cit-vol\u0022\u003E19\u003C\/span\u003E:\u003Cspan class=\u0022cit-fpage\u0022\u003E579\u003C\/span\u003E\u2013\u003Cspan class=\u0022cit-lpage\u0022\u003E85\u003C\/span\u003E.\u003C\/cite\u003E\u003C\/div\u003E\u003Cdiv class=\u0022cit-extra\u0022\u003E\u003Ca href=\u0022{openurl}?query=rft.jtitle%253DPharmacoepidemiology%2Band%2Bdrug%2Bsafety%26rft.stitle%253DPharmacoepidemiol%2BDrug%2BSaf%26rft.aulast%253DRuigomez%26rft.auinit1%253DA.%26rft.volume%253D19%26rft.issue%253D6%26rft.spage%253D579%26rft.epage%253D585%26rft.atitle%253DValidation%2Bof%2Bischemic%2Bcerebrovascular%2Bdiagnoses%2Bin%2Bthe%2Bhealth%2Bimprovement%2Bnetwork%2B%2528THIN%2529.%26rft_id%253Dinfo%253Adoi%252F10.1002%252Fpds.1919%26rft_id%253Dinfo%253Apmid%252F20131328%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-openurl cit-ref-sprinkles-open-url\u0022\u003E\u003Cspan\u003EOpenUrl\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=10.1002\/pds.1919\u0026amp;link_type=DOI\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-doi cit-ref-sprinkles-crossref\u0022\u003E\u003Cspan\u003ECrossRef\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=20131328\u0026amp;link_type=MED\u0026amp;atom=%2Fbmjopen%2F1%2F1%2Fe000025.atom\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-medline\u0022\u003E\u003Cspan\u003EPubMed\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=000279387300007\u0026amp;link_type=ISI\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-newisilink cit-ref-sprinkles-webofscience\u0022\u003E\u003Cspan\u003EWeb of Science\u003C\/span\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\u003Cli\u003E\u003Ca class=\u0022rev-xref-ref\u0022 href=\u0022#xref-ref-6-1\u0022 title=\u0022View reference 9 in text\u0022 id=\u0022ref-9\u0022\u003E\u21b5\u003C\/a\u003E\u003Cdiv class=\u0022cit ref-cit ref-journal\u0022 id=\u0022cit-1.1.e000025.9\u0022\u003E\u003Cdiv class=\u0022cit-metadata\u0022\u003E\u003Col class=\u0022cit-auth-list\u0022\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003ECharlton\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003ERA\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003EWeil\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EJG\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003ECunnington\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EMC\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-etal\u0022\u003Eet al\u003C\/span\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Ccite\u003E. \u003Cspan class=\u0022cit-article-title\u0022\u003EIdentifying major congenital malformations in the UK General Practice Research Database (GPRD) a study reporting on the sensitivity and added value of photocopied medical records and free text in the GPRD\u003C\/span\u003E. \u003Cabbr class=\u0022cit-jnl-abbrev\u0022\u003EDrug Saf\u003C\/abbr\u003E \u003Cspan class=\u0022cit-pub-date\u0022\u003E2010\u003C\/span\u003E;\u003Cspan class=\u0022cit-vol\u0022\u003E33\u003C\/span\u003E:\u003Cspan class=\u0022cit-fpage\u0022\u003E741\u003C\/span\u003E\u2013\u003Cspan class=\u0022cit-lpage\u0022\u003E50\u003C\/span\u003E.\u003C\/cite\u003E\u003C\/div\u003E\u003Cdiv class=\u0022cit-extra\u0022\u003E\u003Ca href=\u0022{openurl}?query=rft.jtitle%253DDrug%2Bsafety%2B%253A%2B%2Ban%2Binternational%2Bjournal%2Bof%2Bmedical%2Btoxicology%2Band%2Bdrug%2Bexperience%26rft.stitle%253DDrug%2BSaf%26rft.aulast%253DCharlton%26rft.auinit1%253DR.%2BA.%26rft.volume%253D33%26rft.issue%253D9%26rft.spage%253D741%26rft.epage%253D750%26rft.atitle%253DIdentifying%2Bmajor%2Bcongenital%2Bmalformations%2Bin%2Bthe%2BUK%2BGeneral%2BPractice%2BResearch%2BDatabase%2B%2528GPRD%2529%253A%2Ba%2Bstudy%2Breporting%2Bon%2Bthe%2Bsensitivity%2Band%2Badded%2Bvalue%2Bof%2Bphotocopied%2Bmedical%2Brecords%2Band%2Bfree%2Btext%2Bin%2Bthe%2BGPRD.%26rft_id%253Dinfo%253Apmid%252F20701407%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-openurl cit-ref-sprinkles-open-url\u0022\u003E\u003Cspan\u003EOpenUrl\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=20701407\u0026amp;link_type=MED\u0026amp;atom=%2Fbmjopen%2F1%2F1%2Fe000025.atom\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-medline\u0022\u003E\u003Cspan\u003EPubMed\u003C\/span\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\u003Cli\u003E\u003Ca class=\u0022rev-xref-ref\u0022 href=\u0022#xref-ref-10-1\u0022 title=\u0022View reference 10 in text\u0022 id=\u0022ref-10\u0022\u003E\u21b5\u003C\/a\u003E\u003Cdiv class=\u0022cit ref-cit ref-journal\u0022 id=\u0022cit-1.1.e000025.10\u0022 data-doi=\u002210.1038\/sj.bjc.6605593\u0022\u003E\u003Cdiv class=\u0022cit-metadata\u0022\u003E\u003Col class=\u0022cit-auth-list\u0022\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003ETate\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EAR\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003ENicholson\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EAC\u003C\/span\u003E\u003C\/span\u003E, \u003C\/li\u003E\u003Cli\u003E\u003Cspan class=\u0022cit-auth\u0022\u003E\u003Cspan class=\u0022cit-name-surname\u0022\u003ECassell\u003C\/span\u003E \u003Cspan class=\u0022cit-name-given-names\u0022\u003EJA\u003C\/span\u003E\u003C\/span\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003Ccite\u003E. \u003Cspan class=\u0022cit-article-title\u0022\u003EAre GPs under-investigating older patients presenting with symptoms of ovarian cancer? Observational study using General Practice Research Database\u003C\/span\u003E. \u003Cabbr class=\u0022cit-jnl-abbrev\u0022\u003EBr J Cancer\u003C\/abbr\u003E \u003Cspan class=\u0022cit-pub-date\u0022\u003E2010\u003C\/span\u003E;\u003Cspan class=\u0022cit-vol\u0022\u003E102\u003C\/span\u003E:\u003Cspan class=\u0022cit-fpage\u0022\u003E947\u003C\/span\u003E\u2013\u003Cspan class=\u0022cit-lpage\u0022\u003E51\u003C\/span\u003E.\u003C\/cite\u003E\u003C\/div\u003E\u003Cdiv class=\u0022cit-extra\u0022\u003E\u003Ca href=\u0022{openurl}?query=rft.jtitle%253DBritish%2BJournal%2Bof%2BCancer%26rft.stitle%253DBritish%2BJournal%2Bof%2BCancer%26rft.aulast%253DTate%26rft.auinit1%253DA.%2BR.%26rft.volume%253D102%26rft.issue%253D6%26rft.spage%253D947%26rft.epage%253D951%26rft.atitle%253DAre%2BGPs%2Bunder-investigating%2Bolder%2Bpatients%2Bpresenting%2Bwith%2Bsymptoms%2Bof%2Bovarian%2Bcancer%253F%2BObservational%2Bstudy%2Busing%2BGeneral%2BPractice%2BResearch%2BDatabase.%26rft_id%253Dinfo%253Adoi%252F10.1038%252Fsj.bjc.6605593%26rft_id%253Dinfo%253Apmid%252F20197770%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-openurl cit-ref-sprinkles-open-url\u0022\u003E\u003Cspan\u003EOpenUrl\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=10.1038\/sj.bjc.6605593\u0026amp;link_type=DOI\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-doi cit-ref-sprinkles-crossref\u0022\u003E\u003Cspan\u003ECrossRef\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=20197770\u0026amp;link_type=MED\u0026amp;atom=%2Fbmjopen%2F1%2F1%2Fe000025.atom\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-medline\u0022\u003E\u003Cspan\u003EPubMed\u003C\/span\u003E\u003C\/a\u003E\u003Ca href=\u0022\/lookup\/external-ref?access_num=000275635900002\u0026amp;link_type=ISI\u0022 class=\u0022cit-ref-sprinkles cit-ref-sprinkles-newisilink cit-ref-sprinkles-webofscience\u0022\u003E\u003Cspan\u003EWeb of Science\u003C\/span\u003E\u003C\/a\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\u003C\/ol\u003E\u003C\/div\u003E\u003Cspan class=\u0022highwire-journal-article-marker-end\u0022\u003E\u003C\/span\u003E\u003C\/div\u003E\u003Cspan id=\u0022related-urls\u0022\u003E\u003C\/span\u003E\u003C\/div\u003E\u003Ca href=\u0022https:\/\/bmjopen.bmj.com\/content\/1\/1\/e000025.abstract\u0022 class=\u0022hw-link hw-link-article-abstract\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EView Abstract\u003C\/a\u003E\u003C\/div\u003E \u003C\/div\u003E\n\n \n \u003C\/div\u003E\n\u003Cdiv class=\u0022panel-separator\u0022\u003E\u003C\/div\u003E\u003Cdiv class=\u0022panel-pane pane-highwire-article-data-supp\u0022 id=\u0022supplementary-materials\u0022\u003E\n \n \u003Ch2 class=\u0022pane-title\u0022\u003ESupplementary materials\u003C\/h2\u003E\n \n \n \u003Cdiv class=\u0022pane-content\u0022\u003E\n \u003Cdiv class=\u0022item-list\u0022\u003E\u003Cul\u003E\u003Cli class=\u0022first last\u0022\u003E\u003Cdiv class=\u0022highwire-markup\u0022\u003E\u003Cdiv xmlns=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022 id=\u0022content-block\u0022 xmlns:xhtml=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022\u003E\u003Cdiv\u003E\u003Cspan class=\u0022highwire-journal-article-marker-start\u0022\u003E\u003C\/span\u003E\u003Cdiv class=\u0022auto-clean\u0022\u003E\u003Cspan style=\u0022font-family: Verdana,Arial,Helvetica,sans-serif; font-size: 83.33%\u0022\u003E\n \n \u003Ch2\u003ESupplementary Data bmjopen-2010-000025\u003C\/h2\u003E\n \u003Cp\u003E\u003Cstrong\u003EFiles in this Data Supplement:\u003C\/strong\u003E\u003C\/p\u003E\n \u003Cul\u003E\u003Cli\u003E\u003Ca href=\u0022\/highwire\/filestream\/93846\/field_highwire_adjunct_files\/0\/bmjopen_research_checklist_000025.pdf\u0022 class=\u0022rewritten\u0022 data-icon-position=\u0022\u0022 data-hide-link-title=\u00220\u0022\u003EView Research Checklist\u003C\/a\u003E \n \t\t\n \u003C\/li\u003E\u003C\/ul\u003E\n \u003C\/span\u003E\n \n \u003C\/div\u003E\u003Cspan class=\u0022highwire-journal-article-marker-end\u0022\u003E\u003C\/span\u003E\u003C\/div\u003E\u003Cspan id=\u0022related-urls\u0022\u003E\u003C\/span\u003E\u003C\/div\u003E\u003C\/div\u003E\u003C\/li\u003E\n\u003C\/ul\u003E\u003C\/div\u003E \u003C\/div\u003E\n\n \n \u003C\/div\u003E\n\u003Cdiv class=\u0022panel-separator\u0022\u003E\u003C\/div\u003E\u003Cdiv class=\u0022panel-pane pane-highwire-markup footnotes\u0022 \u003E\n \n \n \n \u003Cdiv class=\u0022pane-content\u0022\u003E\n \u003Cdiv class=\u0022highwire-markup\u0022\u003E\u003Cdiv xmlns=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022 id=\u0022content-block-markup\u0022 xmlns:xhtml=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022\u003E\u003Cdiv xmlns:xhtml=\u0022http:\/\/www.w3.org\/1999\/xhtml\u0022 class=\u0022section fn-group\u0022 id=\u0022fn-group-1\u0022\u003E\u003Ch2\u003EFootnotes\u003C\/h2\u003E\u003Cul\u003E\u003Cli class=\u0022fn-other\u0022 id=\u0022fn-1\u0022\u003E\u003Cp id=\u0022p-1\u0022\u003E\u003Cstrong\u003ETo cite:\u003C\/strong\u003E Tate AR, Martin AGR, Ali A, \u003Cem\u003Eet al\u003C\/em\u003E. Using free text information to explore how and when GPs code a diagnosis of ovarian cancer: an observational study using primary care records of patients with ovarian cancer. \u003Cem\u003EBMJ Open\u003C\/em\u003E 2011;\u003Cstrong\u003E1\u003C\/strong\u003E:e000025. doi:\u003Ca href=\u0022http:\/\/dx.doi.org\/10.1136\/bmjopen-2010-000025\u0022\u003E10.1136\/bmjopen-2010-000025\u003C\/a\u003E\u003C\/p\u003E\u003C\/li\u003E\u003Cli class=\u0022fn-financial-disclosure\u0022 id=\u0022fn-4\u0022\u003E\u003Cp id=\u0022p-60\u0022\u003E\u003Cspan class=\u0022fn-label\u0022\u003EFunding\u003C\/span\u003E This work was supported by the Wellcome Trust (086105\/Z\/08\/Z). Access to the General Practice Research Database was funded through the Medical Research Council\u0027s licence agreement with Medicines and Healthcare Products Regulatory Agency (MHRA). The authors were independent from the funder and sponsor, who had no role in the conduct, analysis or the decision to publish. This study is based in part on data from the Full Feature General Practice Research Database obtained under licence from the UK MHRA. However, the interpretation and conclusions contained in this study are those of the authors alone.\u003C\/p\u003E\u003C\/li\u003E\u003Cli class=\u0022fn-conflict\u0022 id=\u0022fn-5\u0022\u003E\u003Cp id=\u0022p-61\u0022\u003E\u003Cspan class=\u0022fn-label\u0022\u003ECompeting interests\u003C\/span\u003E None.\u003C\/p\u003E\u003C\/li\u003E\u003Cli class=\u0022fn-other\u0022 id=\u0022fn-6\u0022\u003E\u003Cp id=\u0022p-62\u0022\u003E\u003Cspan class=\u0022fn-label\u0022\u003EEthics approval\u003C\/span\u003E Access to the dataset was approved by the Independent Scientific Advisory Committee (protocol 07 069).\u003C\/p\u003E\u003C\/li\u003E\u003Cli class=\u0022fn-participating-researchers\u0022 id=\u0022fn-7\u0022\u003E\u003Cp id=\u0022p-63\u0022\u003E\u003Cspan class=\u0022fn-label\u0022\u003EContributors\u003C\/span\u003E ART conceived and wrote the paper, read and classified the free text, and carried out the subsequent analysis. AGRM devised the classification scheme, read through and classified the free text, wrote part of the paper, and provided expert advice. JAC was involved in the conception and writing of the paper. AA participated in writing the paper (including the literature review) and assisted with data management. All authors had full access to all of the data (including statistical reports and tables) in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis. 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